Polaris Sportsman 850SP Owner's Manual page 109

MAINTENANCE
Spark Plugs
Spark Plug Inspection
Normal Spark Plug
The normal insulator tip is gray, tan or light brown. There will be few
combustion deposits. The electrodes are not burned or eroded. This
indicates the proper type and heat range for the engine and the service.
The tip should not be flaky and white. A white insulator tip indicates
overheating, caused by use of an improper spark plug or incorrect fuel.
Wet Fouled Spark Plug
The wet fouled insulator tip is black. A damp oil film covers the firing
end. There may be a carbon layer over the entire nose. Generally, the
electrodes are not worn. General causes of fouling are excessive oil, use
of non-recommended oil or incorrect throttle body adjustments.
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